Gas separation process using membranes with permeate sweep to remove co2 from combustion gases
a gas separation and gas technology, applied in the field of membrane-based gas separation processes, can solve the problems of power plants producing enormous amounts of flue gas, and achieve the effect of maintaining or enhancing the beneficial effect of copermeation of water
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example 1
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[0116](a) Membrane permeation experiments: A set of permeation experiments was performed with a composite membrane having a polyether-based selective layer. The properties of the membrane as measured with a set of pure gases at 6.7 bar absolute and 30° C. are shown in Table 1.
TABLE 1PermeanceCO2 / GasGas(gpu)*SelectivityCarbon dioxide1,000 —Nitrogen2050Oxygen5020Methane5020Water>2,000** —*Gas permeation unit; 1 gpu = 1 × 10−6 cm3(STP) / cm2 · s · cmHg**Estimated, not measured
[0117](b) Assumptions concerning power plant: All calculations were performed assuming that the flue gas to be treated was from a 600 MW gross power coal-fired power plant. It was assumed that the exhaust gas is filtered to remove fly ash and other particulate matter before passing to the membrane separation steps.
[0118]The assumed compositions of the coal and air feed, and the calculated composition of the flue gas based on conventional combustion are shown in Table 2.
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example 2
Not in Accordance with the Invention
[0120]A calculation was performed to illustrate the treatment of the flue gas by membrane separation without using a sweep gas on the permeate side. It was assumed that the flue gas was (i) compressed to 9 bar, (ii) cooled to 30° C., and (iii) subjected to membrane separation using only the total pressure difference and ratio to achieve the separation. The permeate side of the membranes was assumed to be maintained at 1 bar.
[0121]Part of the compression requirement was assumed to be met by expanding the membrane residue stream back to 1 bar before discharge.
[0122]The results of the calculations are shown in Table 3.
TABLE 3MembraneRaw flueMembraneresidue / MembraneComponent / Parametergasfeedvent gaspermeateFlow rate(MMscfd)1,5001,354970384Flow rate2,2932,1511,453698(thousand kg / h)Temperature (° C.)50302920Pressure (bar)1.099957Component (mol %)Carbon dioxide11.612.71.840.3Oxygen4.34.74.25.9Nitrogen73.882.294.052.2Water10.20.40.01.5
[0123]As can be seen...
example 3
Not in Accordance with the Invention
[0131]A second calculation was performed to illustrate the treatment of the flue gas by membrane separation without using a sweep gas on the permeate side. This time it was assumed that the flue gas was passed across the feed side without compression, but after cooling to 30° C., and that a vacuum of 0.2 bar was pulled on the permeate side of the membranes.
[0132]The results of the calculations are shown in Table 4.
TABLE 4MembraneRaw flueMembraneresidue / MembraneComponent / Parametergasfeedvent gaspermeateFlow rate(MMscfd)1,5001,403865539Flow rate2,2932,2021,294907.6(thousand kg / h)Temperature (° C.)50302929Pressure (bar)1.11.11.10.2Component (mol %)Carbon dioxide11.612.42.029.1Oxygen4.34.53.75.7Nitrogen73.879.293.756.0Water10.23.90.59.2
[0133]The process again achieves 90% carbon dioxide removal, from 174 to 17 MMscfd in the discharged flue gas, and cuts the concentration of carbon dioxide in the exhaust stream to 2 vol %.
[0134]The calculated membrane ...
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